The present invention relates to an apparatus for continuously measuring the change in the concentration of a pigment in blood in a living tissue.
A technique known as pulse oximetry is capable of measuring the concentration of a pigment in the arterial blood in a living tissue in a noninvasive and continuous manner. However, the number of measurements that can be attained by this technique per heart beat is usually one, and no more than a few at maximum. This is because in order to attain one value of measurement by pulse oximetry, it is necessary to detect the quantity of light that has been transmitted through a pulsating blood at least two points of time, which must be kept apart by a certain amount in order to ensure a correct value of measurement.
The technique of pulse oximetry has the disadvantage that when the oxygen saturation of blood changes very rapidly or in such a case where the cardiac output is to be calculated from a pigment dilution curve constructed by injecting a pigment into a blood vessel, it is impossible to measure the change in the concentration of the pigment in a fully continuous manner regardless of the cycle of heart beats.
The present invention has been accomplished in order to eliminate this defect of the prior art technique. An object, therefore, of the present invention is to provide an apparatus capable of measuring the concentration of a pigment in blood in a noninvasive and fully continuous manner.